Compositions involving V2 O3 -ZRO2 -TIO2

ABSTRACT

The present invention pertains to novel solid solutions involving V 2  O 3 , ZrO 2  and TiO 2  and the method for their preparation. The compositions involving V 2  O 3 , ZrO 2  and TiO 2  fall within the shaded area of a polygon in a ternary composition diagram of V 2  O 3 , ZrO 2  and TiO 2  as shown in the drawing herein e.g., FIG. 1. These materials may be used as an oxidation catalyst or in the manufacture of high temperature refractories.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to compositions involving V₂ O₃ -ZrO₂ -TiO₂.

SUMMARY OF THE INVENTION

The present invention pertains to novel solid solutions involving V₂ O₃,ZrO₂ and TiO₂ and the method for their preparation. The solidcompositions involving V₂ O₃, ZrO₂ and TiO₂ fall within the shaded areaof a polygon in a ternary composition diagram of V₂ O₃, ZrO₂ and TiO₂ asshown in the drawing herein e.g. FIG. 1. The polygon has the verticesand corresponding coordinates in weight percent as shown in thefollowing Table I.

                  TABLE I                                                         ______________________________________                                                Coordinates (wt %)                                                    Vertices  V.sub.2 O.sub.3                                                                             ZrO.sub.2                                                                             TiO.sub.2                                     ______________________________________                                        A         50            50       0                                            B         24            50      26                                            C         24            10      66                                            D         32             2      66                                            F         98             2       0                                            ______________________________________                                    

The compositions involving V₂ O₃, ZrO₂ and TiO₂ are depicted by theshaded area circumscribed by ABCDF as shown in FIG. 1. These novel solidsolutions involving V₂ O₃, ZrO₂ and TiO₂ are made by the processinvolving the steps of:

(1) heating V₂ O₅ powder having a particle size of less than about 50microns in an atmosphere in which the partial pressure of oxygen is inthe range of 10⁻⁸ to 10⁻¹⁰ atmosphere while gradually increasing thetemperature stepwise over a temperature range of about 600° C. to 1300°C., and holding the temperature at about 1300° C. for a period to ensurecomplete reduction of all vanadium to V³⁺ ;

(2) heating TiO₂ and ZrO₂ powders each having a particle size of lessthan about 50 microns for a period of about 10 to 14 hrs. at atemperature in the range of about 600° C. to 800° C. for TiO₂ and about1000° C. to 1200° C. for ZrO₂ ;

(3) thoroughly grinding together about 24 to 98 wt. % of V₂ O₃ from (1),with about 2 to 50 wt. % of ZrO₂ and about 0 to 66 wt. % of TiO₂ from(2) to produce a mixture having a grain size of less than about 50microns,

(4) pelletizing the mixture from (3) at a pressure of about 5,000 psi;and

(5) heating and reacting together the pellets from (4) at a temperaturein the range of about 1100° C. to 1700° C. for a period in the range ofabout 1/2 to 48 hrs., in an atmosphere in which the partial pressure ofoxygen is in the range of 10⁻¹⁰ to 10⁻⁵ atmosphere to produce saidcompositions involving V₂ O₃, ZrO₂ and TiO₂.

In one embodiment, the pellets from step (5) are cooled to ambienttemperature while at substantially the same partial pressure of oxygenas in step (5). Preferably, to prevent undue oxidation and moisturepickup, the cooled pellets are stored in a sealed container.

BRIEF DESCRIPTION OF THE DRAWING

The drawing e.g. FIG. 1 depicts a ternary composition diagram showing apolygon shaped shaded area circumscribed by ABCDF within which usefulcompositions involving V₂ O₃ -ZrO₂ -TiO₂ are found.

DESCRIPTION OF THE INVENTION

New solid solutions have been synthesized by the subject invention inwhich the nature and extent of the formation of solid solutionsinvolving V₂ O₃, ZrO₂ and TiO₂ have been characterized. This work hasled to synthesizing new phases in which vanadium in several oxidationstates are accommodated such as to render crystalline phasesthermodynamically stable over a wide range of oxygen pressures atelevated temperatures.

The newly synthesized solid compositions involving V₂ O₃ -ZrO₂ -TiO₂ areshown in the enclosed figure (drawing) as circumscribed by the polygonshaped shaded area ABCDF in the ternary composition diagram. Theoxidation states of vanadium in the solid solutions are mainly +3 and+4.

The polygon shaped shaded area has the following vertices andcorresponding coordinates in weight percent:

    ______________________________________                                                Coordinates (wt %)                                                    Vertices  V.sub.2 O.sub.3                                                                             ZrO.sub.2                                                                             TiO.sub.2                                     ______________________________________                                        A         50            50       0                                            B         24            50      26                                            C         24            10      66                                            D         32             2      66                                            F         98             2       0                                            ______________________________________                                    

A typical newly synthesized composition involving V₂ O₃, ZrO₂ and TiO₂having the formula Zr₀.11 V₁.89 Ti₀.83 O₅.00 is illustrated by point Gin the drawing having the following coordinates in wt. %: V₂ O₃ 64, ZrO₂6, and TiO₂ 30.

The subject compositions made from V₂ O₃, ZrO₂ and TiO₂ are synthesizedin the following manner. The identity of the reaction product, solidsolutions involving V₂ O₃ -ZrO₂ -TiO₂, may be confirmed by X-raydiffraction analysis.

First, V₂ O₃ is prepared by heating commercially availableanalytical-grade V₂ O₅ having a particle size of less than about 50microns in a vertical tube furnace in an atmosphere of carefullyselected oxygen pressure within the stability range of V₂ O₃ e.g. in therange of 10⁻⁸ to 10⁻¹⁰ atmospheres. This is accomplished by using a gasmixture of high-purity e.g. 99.9 mole% or more CO₂ and H₂ or CO₂ and COor H₂ O and H₂ in controlled proportions. The CO₂ /H₂, CO₂ /CO or H₂O/H₂ ratio by volume is in the range of 10/1 to 1/1. The relatively lowmelting point of the starting vanadium oxide (V₂ O₅) e.g. about 690° C.,necessitates heating the oxide slowly. Starting at a temperature ofabout 600° C., the temperature is gradually increased stepwise over aperiod of about 12 to 24 hrs. to a final temperature of about 1300° C.At a temperature of about 1300° C. the vanadium oxide is held at leastabout 24 hrs e.g. 24 to 30 hrs. to ensure complete reduction of allvanadium to V³⁺.

Preheated analytical-grade oxides having a particle size of less thanabout 50 microns are used as starting materials for the other componentsof the solid solutions to be synthesized. For example, TiO₂ is heatedfor about 10 to 14 hrs. at a temperature in the range of about 600° C.to 800° C. and ZrO₂ is heated for about 10 to 14 hrs. at a temperaturein the range of about 1000° C. to 1200° C. prior to being used inpreparation of the final mixtures. The oxides are thereby demoisturized.They may be then cooled to ambient conditions.

The mixtures of the three oxide components are thoroughly mechanicallyground together under acetone in a an agate mortar to ensure thoroughmixing and a sufficiently small grain size e.g. less than 50 microns.For example, about 24 to 98 wt. % of V₂ O₃ is ground together with about2 to 50 wt. % of ZrO₂ and about 0 to 66 wt. % of TiO₂ to produce amixture having a grain size of less than about 50 microns. Completeformation of the desired compounds in the succeeding heat treatment isthereby promoted. Next, the oxide mixtures are pelletized at a pressureof about 5,000 psi or higher. The pellets may have any conventional sizee.g. 1/16" to 1". The pellets are then heated and reacted together at atemperature in the range of about 1100° C. to 1700° C., such as about1100° C. to 1200° C., for a period in the range of about 1/2 to 48 hrs.,such as about 1/2 to 2 hrs. (depending on the nature and solidustemperature of the phase to be synthesized) in a vertical tube furnacewith carefully controlled oxygen pressures, in the range of 10⁻¹⁰ to10⁻⁵ atmosphere. In the manner described previously for preparing V₂ O₃,the pellets are heated in a furnace atmosphere provided by a gas mixtureof CO₂ and H₂ or CO₂ and CO or H₂ O and H₂ in various desired volumetricmixing ratios. For example, the volumetric ratio CO₂ /H₂, CO₂ /CO, or H₂O/H₂ is typically in the range of about 10/1 to 1/1. These selectedratios are kept constant for the duration of the synthesis by use of adifferential manometer. By this method the oxygen pressure at thespecified temperature can be controlled to better than ±1%. Thethermodynamic data for the water-gas shift reaction (CO₂ +H₂ =CO+H₂ O),on which the calculations were based, are known with extremely highaccuracy (better than 0.1%). Hence, the method used herein ensuresreliable accurate control of the oxidation state of vanadium during thesynthesis. This is extremely important for optimization of theproperties of the finished product.

At the time of the high temperature reaction in the range of about 1100°C. to 1700° C., all of the oxide pellets may be in the solid state or atleast one, two or three of the oxide constituents may be in the moltenstate. At the reaction conditions prevailing in the subject process,solid solutions may be made by solid-state reactions considerably belowtemperatures at which a liquid phase is present. However, the presenceof a liquid phase or a solid-liquid phase improves the kinetics of thereaction.

The individual oxide components are heated to a sufficiently hightemperature to expel absorbed or adsorbed water. Well defined startingmaterials for accurately weighing up mixtures is thereby produced. V₂ O₅was heated slowly in several steps to a temperature of about 600° C. to1300° C., such as about 1100° C. to 1300° C. at controlled Oxygenpressures in order to preferably decompose the V₂ O₅ slowly to V₂ O₃. Bythis means, violent reactions are avoided at the highest temperatures,and most of the vanadium is produced in the desired oxidation state V³⁺.

The oxide mixtures were heated at temperatures in the range of about1100° C.-1700° C. in order to promote reaction among the oxidecomponents to the desired finished products consisting mainly of one ormore (solid-solution) phases. In one embodiment, the mixture of solidparticles was heated to a temperature below the solidus, for example toabout 1200°. The phase assemblage of the final product was producedentirely by solid state reaction. Under such conditions, the crystalswere relatively small, typically, of about 0.5-3.0 microns. In anotherembodiment, the mixtures were heated to a sufficiently high temperaturee.g. about 1700° C. to produce partial or complete melting. This speedsup the reaction and produces (solid solution) phases (crystals) oflarger size, typically in the range of about 2-100 microns. Afterheating the mixtures at this high temperature for a period of time, suchas 1/2-2 hrs., the composition is cooled to ambient conditions. Forexample, the composition may be cooled slowly (over a period of 1/2-1hr) to about 1200° C. From this temperature, the composition may becooled rapidly (quenched) to room temperature. During these runs theoxygen pressure of the gas phase was controlled by using gas mixtures ofCO₂ and H₂, CO₂ and CO, or H₂ O and H₂ with volumetric ratios CO₂ /H₂,CO₂ /CO or H₂ O/H₂ in the range of about 10/1-1/1.

In addition to oxygen pressure, one other parameter influencing theoxidation state of vanadium in oxide phases has been utilized insynthesizing the new phases. This is the provision of host structureswhich incorporate vanadium in one (or more) valence state(s) in strongpreference to other valence states. In the present case, the ternarysolid solution phase of pseudobrookite structure in the system V₂ O₃-ZrO₂ -TiO₂ serves this purpose. In this solid solution vanadium ispresent partly in the trivalent state, and partly in the tetravalentstate, as stabilized by the preferential substitution of V⁴⁺ for Ti⁴⁺.

The pellets of the composition involving V₂ O₃ -ZrO₂ -TiO₂ may be usedas an oxidation catalyst, offering improved activity and yields andgreater stability over a wider temperature range e.g. about 1000° C. orhigher than that which is offered by typical oxidation catalysts. Forexample, as an oxidation catalyst the subject pellets may be used in theconversion of oxylene to phthalic anhydride, butane to maleic anhydride,or alcohols to aldehydes or organic acids.

As a high temperature refractory or as an ingredient in a hightemperature refractory material for lining a gasifier for the partialoxidation of ash-containing liquid hydrocarbonaceous and solidcarbonaceous fuels, the subject material would have a long life,withstanding attack from V₂ O₅. For example, a thermal refractory forlining the reaction zone of a partial oxidation gas generator maycomprise the previously described composition involving V₂ O₃ -ZrO₂-TiO₂ in the amount of about 1 to 25 wt. %, and the remainder of therefractory e.g. about 75 to 99 wt. % involving oxides with a cationicportion that is selected from the group consisting of Cr, Mg, Al, Mn, Siand mixtures thereof. The partial oxidation reactor operates in areducing atmosphere and at a temperature in the range of about 1700° F.to 3000° F.

The subject composition involving V₂ O₃ -ZrO₂ -TiO₂ may also be used asan additive. About 0.01 to 0.2 wt. % (basis weight of ash in the fuelfed to the gas generator) of additive may be introduced into therefractory lined partial oxidation gas generator along with the fuelfeed to stabilize said refractory.

Various modifications of the invention as herein before set forth may bemade without departing from the spirit and scope thereof, and therefore,only such limitations should be made as are indicated in the appendedclaims.

We claim:
 1. A method of preparing compositions, from V₂ O₃, ZrO₂ andTiO₂ that fall within the shaded area circumscribed by ABCDF as shown inthe disclosed figure, and wherein said method comprises the steps of(1)heating V₂ O₅ powder having a particle size of less than about 50microns in an atmosphere in which the partial pressure of oxygen is inthe range of 10⁻⁸ to 10⁻¹⁰ atmospheres while gradually increasing thetemperature over a temperature range of about 600° C. to 1300° C. andholding the temperature at about 1300° C. for a period to ensurecomplete reduction of all vanadium to V³⁺ ; (2) heating TiO₂ and ZrO₂powders each having a particle size of less than about 50 microns for aperiod of about 10 to 14 hrs. at a temperature in the range of about600° C. to 800° C. for TiO₂ and about 1000° C. to 1200° C. for ZrO₂ ;(3) thoroughly grinding together about 24 to 98 wt. % of V₂ O₃ from (1),with about 2 to 50 wt. % of ZrO₂ and about 0 to 66 wt. % of TiO₂ from(2) to produce a mixture having a grain size of less than about 50microns; (4) pelletizing the mixture from (3) at a pressure of about5,000 psi; and (5) heating and reacting together the pellets from (4) ata temperature in the range of about 1100° C. to 1700° C. for a period inthe range of about 12 to 48 hrs. in an atmosphere in which the partialpressure of oxygen is in the range of 10⁻¹⁰ to 10⁻⁵ atmosphere.
 2. Themethod of claim 1 wherein said figure the amounts of V₂ O₃, ZrO₂ andTiO₂ are characterized as shown in the Table below;

    ______________________________________                                                Coordinates (wt %)                                                    Vertices  V.sub.2 O.sub.3                                                                             ZrO.sub.2                                                                             TiO.sub.2                                     ______________________________________                                        A         50            50       0                                            B         24            50      26                                            C         24            10      66                                            D         32             2      66                                            F         98             2       0                                            ______________________________________                                    


3. The method of claim 1 further comprising cooling the pellets from (5) to ambient temperature, while at substantially the same partialpressure of oxygen as in (5); and storing the cooled pellets in a sealedcontainer.
 4. The method of claim 1 wherein said compositions involvingV₂ O₃, ZrO₂ and TiO₂ are solid solutions.
 5. The method of claim 1wherein at the time of reaction in (5) all of the oxide pellets are inthe solid state or at least one, two or three of the oxide constituentsmay be in the molten state.
 6. The method of claim 1 where in step (1)said V₂ O₅ powder is heated in an atmosphere comprising a gas mixture ofCO₂ and H₂ with a volume ratio of CO₂ /H₂ in the range of about 10/1 to1/1.
 7. The method of claim 1 wherein step (5) said pellets are heatedin an atmosphere comprising a gas mixture of CO₂ and H₂ with a volumeratio of CO₂ /H₂ in the range of about 10/1 to 1/1.
 8. The method ofclaim 1 wherein steps (1) and (5) said materials are heated in anatmosphere comprising a gas mixture of CO₂ and CO or H₂ O and H₂ involumetric ratios CO₂ /CO or H₂ O/H₂ in the range of about 10/1 to 1/1.9. The method of claim 1 wherein said composition has the formula Zr₀.11V₁.89 Ti₀.83 O₅.00 as illustrated by point G in said figure, and havingthe following coordinates in wt. %: V₂ O₃ 64, ZrO₂ 6 and TiO₂
 30. 10.The method of claim 1 wherein said composition has a structure ofpseudobrookite.
 11. Thermal refractory compositions comprising, (1) asolid solution in the amount of about 1-25 wt. %, and (2) at least oneoxide having a cationic portion selected from the group consisting ofCr, Mg, Al, Mn, Si, and mixtures thereof, wherein said solid solution isproduced from V₂ O₃, ZrO₂ and TiO₂ and has a composition that fallswithin the shaded area circumscribed by ABCDF as shown in the disclosedFigure wherein the amounts of V₂ O₃, ZrO₂ and TiO₂ are characterized asshown in the table below:

    ______________________________________                                                Coordinates (Wt %)                                                    Vertices  V.sub.2 O.sub.3                                                                             ZrO.sub.2                                                                             TiO.sub.2                                     ______________________________________                                        A         50            50       0                                            B         24            50      26                                            C         24            10      66                                            D         32             2      66                                            F         98             2       0                                            ______________________________________                                    


12. Compositions produced from V₂ O₃, ZrO₂ and TiO₂, wherein saidcompositions are solid solutions and fall within the shaded areacircumscribed by ABCDF as shown in the disclosed Figure wherein theamounts of V₂ O₃, ZrO₂ and TiO₂ are characterized as shown in the tablebelow:

    ______________________________________                                                Coordinates (Wt %)                                                    Vertices  V.sub.2 O.sub.3                                                                             ZrO.sub.2                                                                             TiO.sub.2                                     ______________________________________                                        A         50            50       0                                            B         24            50      26                                            C         24            10      66                                            D         32             2      66                                            F         98             2       0                                            ______________________________________                                    


13. A composition as provided in claim 12 having the formula Zr₀.11V₁.89 Ti₀.83 O₅.00 as illustrated by point G in said disclosed Figureand having the following coordinates in wt. % V₂ O₃ 64, ZrO₂ 6 and TiO₂30.
 14. Compositions produced from V₂ O₃, ZrO₂ and TiO₂ and in which thevanadium is present in the trivalent and tetravalent states, and thestructure comprises pseudobrookite; wherein said compositions arecharacterized by their ability to catalyze oxidation reactions and whichfall within the shaded area circumscribed by ABCDF as shown in thedisclosed Figure wherein the amounts of V₂ O₃, ZrO₂ and TiO₂ arecharacterized as shown in the table below:

    ______________________________________                                                Coordinates (Wt %)                                                    Vertices  V.sub.2 O.sub.3                                                                             ZrO.sub.2                                                                             TiO.sub.2                                     ______________________________________                                        A         50            50       0                                            B         24            50      26                                            C         24            10      66                                            D         32             2      66                                            F         98             2       0                                            ______________________________________                                    